1. Field of Invention
The present invention relates to an olefin thermoplastic elastomer composition and a coated electric wire. More particularly, the present invention relates to a halogen-free olefin thermoplastic elastomer composition satisfying characteristics such as mechanical strength, electric wire extrusion processability, flexibility, wear resistance, and non-flammability which a material for coating the electric wire for use in a vehicle is required to have. The present invention also relates to the electric wire coated with the halogen-free olefin thermoplastic elastomer composition. The present application claims priority to Japanese Application No. 2002-063237, filed on Mar. 8, 2002.
2. Description of Related Art
Polyvinyl chloride has been mainly used as the material for coating electric wires for use in the vehicle. This is because the polyvinyl chloride is superior in mechanical strength, electric wire extrusion processability, flexibility, colorability, and economy.
However, in consideration of the recent movement for protecting global environment, halogen-free resinous materials have come to be used to manufacture component parts of the vehicle including the electric wire instead of the polyvinyl chloride.
Halogen-free resinous materials are known as wear-resistant resinous materials having an advantage of not generating a poisonous gas such as the halogen gas when it is burnt. The halogen-free resinous materials are formed by adding metal hydroxide to a polyolefin based polymer as a non-flammable agent (Japanese Patent Application Laid-Open Nos. 7-176219, 7-78518).
However, to make the resinous composition non-flammable to such an extent that it has self-extinguishing performance, it is necessary to add a large amount of the metal hydroxide to the polyolefin based polymer. However, the addition of a large amount of the metal hydroxide to the polyolefin based polymer causes the resinous composition to significantly reduce its mechanical strength such as wear resistance, tensile strength, and the like. To avoid reduction of the mechanical strength of the resinous composition, it is conceivable to increase the amount of polypropylene or high-density polyethylene having a comparatively high hardness. In this case, the electric wire coated with the resinous composition has low flexibility and processability.